If Chris Beckett's new novel had turned out to be a bit of a mess, it wouldn't be entirely surprising. Marcher is a fix-up of sorts, its spine grown from a clutch of stories dating back to the early nineties and, for all that I think said stories are among Beckett's best work, at first glance their disparate viewpoints don't appear to lend themselves to being bound together. The connections between stories such as "The Welfare Man" (1993), "To Become a Warrior" (2002), and "Tammy Pendant" (2004) are relatively loose; they share concerns, and elements of their setting, but not characters or (you might think) direct continuity. Between them they sketch a Britain in which the exclusion of the poor and disadvantaged from the rest of society has been formalized; council housing estates have been institutionalized, in an alarming reinforcement of existing class boundaries. What marks the stories out, to my mind, is the sense that they look at characters both inside and outside the estates through eyes that are sympathetic but clear, scathing the system and the vicious circles it perpetuates without, as they say, condoning or condemning individuals. To add to this already-provocative setup mysterious blue pills, usually known as "seeds" or "slip", that allow one-way travel between different timelines, may seem unnecessarily garish; in fact it is what knits the stories, and the novel, into an ingenious and un-messy whole. Slip, as one user—or "shifter"—puts it, offers "all the benefits of suicide and none of the drawbacks" (p. 75); that is, it offers the kind of freedom that only an ability to completely escape the consequences of your actions can provide. And for the inhabitants of what, in Marcher's version of the setting, are known as Social Inclusion Zones, it offers a plausible, if irreversible, way out of desperate conditions.

The three stories I named above are all re-shaped to Marcher's purposes, and the novel has ties to at least another half-dozen of Beckett's tales; but those re-shapings and ties are cannier than is the case in most fix-ups. Probably the most transparent resemblance is (not surprisingly) with the story "Marcher" (2001). Charles Bowen, Marcher's protagonist and narrator, spends the first third of the novel tracing a version of the arc traced by the protagonist of that story, rewritten from third-person to first. An immigration officer of the inter-dimensional kind, Bowen is sent to interview a shifter detained in one of greater Bristol's Zones, Thurston Meadows, but finds himself drawn into another case, the disappearance of a teenage girl, and presented with the opportunity to steal some slip for himself. The story ends with his narrative splintering into three possibilities: in the novel, Beckett picks one and carries on. Meanwhile, the worlds of Beckett's other stories are being slotted into place. Some, most notably "The Welfare Man" and its sequel, "The Welfare Man Retires" (2000), are reproduced more or less wholesale, albeit interspersed with other events; Cyril Burkitt, the aging civil servant who doesn't quite know how he's ended up maintaining a system that goes against everything he stands for, remains a memorable and nuanced character. With these stories, Beckett even keeps the third person, introducing an inspired conceit to account for it. Proximity to shifters, it seems, causes shifts in perspective—visions, hallucinations, flashes of other peoples' memories, even other timeline's events—known as "switches".

As is probably obvious, though it surely wasn't intentional, the novel's history is apt for its subject matter. It's easy to see the earlier stories, with their variations in terminology or plot, as parallel worlds of their own, and the freedom Beckett gives himself to shift point of view reinforces that idea. Indeed, in some cases it's made explicit. In the novel, Tammy Pendant, a teenager living in Thurston Meadows, prostitutes herself to a shifter to acquire some slip, then becomes the disappearance that Bowen ends up investigating. In a switch that takes place shortly afterwords, Tammy's social worker, Jazamine Bright, perceives a timeline in which Tammy is caught, and has her stomach pumped, before the slip can take effect: this is the ending of "Tammy Pendant," which otherwise is basically the same as the version of Tammy's story which appears in the novel. Other small changes in opportunity or circumstance, and their potential to lead to radically different outcomes for the affected characters, are also considered. Bowen and Jazamine speculate on Tammy's fate if she had been adopted, as she nearly was, we are told, save for a last-minute change of heart on the part of her birth mother. That fate, in which Tammy becomes Jessica, brought up in a comfortably middle-class area of London, is seen in "The Turing Test" (2002) and "We Could be Sisters" (2003), although not in the novel. (Equally, versions of Tammy who may be descended from the novel's escapee crop up in other stories, such as last year's "Poppyfields.") Meanwhile, Carl Bone, another Thurston Meadows youth, is recruited into a worldline-spanning cult who worship a version of the Norse pantheon, drawn by the promise of ultimate freedom; his story was first told in "To Become a Warrior," but is here recast from first-person to third, and framed as another switch, this time on the part of Bowen.

All of this perhaps seems a touch dry to those not already familiar with Beckett's work, but quite the opposite is the case. Marcher is something like a tapestry, different threads of incident and character braiding together to produce a greater picture. Switches are a device that allows Beckett to re-use material, but not an excuse for him to do so. That is to say they do work, often double or triple work: succeeding as narrative, while referencing a penumbra of material that emphasizes the instability of any story taking place in a multiverse, and while, within the frame of the novel, playing into and deepening its central theme, which I take to be the construction and necessity of borders. Indeed, the novel's most obvious flaw, to my mind, is that it's just a little too eager to highlight its themes, and their iterations. It's an extremely readable, dialogue-driven book (if, in this edition, unfortunately typo-riddled), but there are few too many on-the-nose lines. I don't mind, for instance, that there's an establishing conversation that gives Bowen the chance to set out his stall—"a country does need a boundary of some sort. An entity of any kind needs a boundary, or ... it just becomes part of the medium that surrounds it and ceases to be a thing in its own right. And if a country has a boundary, it means that some people who want to come in will have to be turned away" (p. 14)—but I don't need all the variations on this theme as it pertains to individuals and society to be explicitly pointed out. ("Someone has to be outside and surplus to requirements so the rest of us can be secure and comfortable inside" [p. 117]; "the economy needs a certain level of unemployment" [p. 168].) I don't need Bowen to have a conversation with a therapist in which he explains his motivations, while in return she explains the "absolute centrality" of subjectivity; nor do I need, as the situation in Thurston Meadows escalates, comparisons to Warsaw and Auschwitz. At such moments, the novel can feel thinner than it actually is.

What works about the novel, on the other hand, works very nicely indeed. Bowen himself is a well-shaded protagonist, sympathetic but with some unappealing tendencies. He's deeply cautious and a stickler for rules, and more than a little pleased with himself for what he sees as his superior insight into the nature of reality, but which is as much as anything a lack of empathy. When Thurston Meadows social workers deny the existence of shifters, he feels contempt: "What they were worried about was purely and simply that they were going to be criticised for not following procedures" (p. 54). Nor is he immune to the escalating conflation of shifter and Zone resident that drives Marcher's plot. His previous girlfriend left him for being "a man who saw nothing but projections of himself" (p. 32), and most of his interactions with women have a hesitant, awkward edge to them, with just a hint of unconscious misogyny. Of necessity he is also a somewhat reactive character; yet despite all this we do, ultimately, care enough to want to see him overcome his internal borders. Of the other characters, I've already mentioned Cyril Burkitt. Jazamine Bright, the social worker, is perhaps slightly less convincing, perhaps never quite escapes her role as Bowen's girlfriend. Tammy Pendant, on the other hand, works as well here as in her original short story appearance: already a kind of shifter in her impatience with social workers and therapists, she is well aware that the power that comes from her youth and attractiveness is the only kind of power she has. The toughness of her upbringing is clear, as is how that toughness has shaped her. The same is true for Carl Bone, though he is a more tragic character, more willing to let himself be shaped by others in pursuit of his chance of escape; a scene in which he talks himself into murder, to prove himself one of the gang, is a bleak tour-de-force.

And in the murder scene itself, among others, Beckett is able to invoke the pluralizing, decentralizing elements of many-worlds theory without, despite what the over-enthusiastic blurb may lead you to expect, turning his narrative into a world-hopping adventure. This, I think, is why Marcher is a significant contribution to its subgenre—even in the face of the stiff competition published in the last few years, which includes such very good novels as Paul McAuley's Cowboy Angels (2007), with its viciously political satire of the idea that there could be such a thing as a "prime" universe, not to mention other books that have used the device to look at the character of a nation, or to explore more abstractly philosophical questions. Beckett does a bit of all three, but the simmering awareness of social injustice is most notable, more authentic than any Barleypunk hyperbole. (Although I think you could argue that the situation portrayed is not quite as culturally diverse as modern Britain deserves.) There is a sense in which this long-gestated book could itself come from an alternate world, one in which the late-nineties boom in British SF took a less pyrotechnic form, focused more on average lives and small stories, the tone set, perhaps, by the early parts of Gwyneth Jones' Kairos (1988) rather than Consider Phlebas (1987). Much as I like pyrotechnics, I wish a few more books from that timeline would slip into ours. One of the things Marcher is good on, for example, is the day-to-day reality of social work; a scene in which Cyrill Burkitt presides over a Zone inhabitant's petition to be released—that's the only word for it—into the general population is riveting, while the frustrations and consolations of the routines of Bowen's job are convincingly drawn.

As are, inevitably, its borders. There are many separate worlds in Marcher, and each of them has its own story to be told. And in a multiverse, of course, every decision leads to more stories, irreversible divergence; which is probably why Marcher doesn't converge in the way that you expect a novel to converge. Resolutions are partial or refused. The departure of characters from the narrative is often abrupt, sometimes devastating, and feels all the more wrong because Beckett has spent more time developing them than you would usually expect a character destined to be so briskly disposed of to receive. This could be seen as evidence of the novel's fix-up roots, except that the most permanent departures don't originate in the stories: originally, Tammy didn't escape, after all. So it feels to me more like evidence of craft, more like a deliberate choice on Beckett's part. Bowen is the closest thing to a stable point in the book, and his perspective, thanks to an increasing number and intensity of switches, becomes increasingly unreliable. One character, late on, describes him as "dissolving," which we may never quite believe—Beckett's portrayals of consciousness remain within the realm of the conventional—but which certainly draws our attention to the way in which Bowen is forcibly gaining the empathy, the ability to see another perspective, that he earlier lacked. (Everyone is their own world.) And Bowen's final decision, fittingly for this multifarious book, certainly opens out his character to interpretation: you can see his last action as either an escape, or a transgression, or a release, or a capitulation. Which you choose, of course, depends on your point of view.

Niall Harrison (niall.harrison@gmail.com) has reviewed for The New York Review of Science Fiction, Foundation, and The Internet Review of Science Fiction, among other places. He blogs at Torque Control.